Help! Suddenly I Can't boot. No recovery; No safe boot; verbose: AppleKeyStore operation failed

Hi,

I have trusty old 17" Macbook Pro from 2011. It's had its hard drive and ram upgraded years ago and all worked well until recently. I've been letting my 1st grader use it for virtual learning so I don't quite know exactly what happened but it was working fine one day and all of a sudden i can't get it to boot.

I've tried doing all of the following options with 2 different SSDs (Samsung EVO 840 and Samsung EVO 860) that have both ran this computer in the past. In either case i get the same results:

Steps I've tried:

• Resetting the SMC
• Resetting the PRAM
• Recovery mode (gets to 1/2 progress bar then blank gray screen)
• Internet Recovery mode (gets past firt loading bar with countdown secs, then goes to black screen and no further progress)
• Boot from USB with OSX Installer (started reading USB since i have lights on it to confirm but then went to black screen and stopped)
• Safe boot (gets to 1/3 progress bar then blank gray screen)
• Safe boot with verbose output (flashes some data including AppleKeyStore error then goes to gray screen) See attached screen grab showing:

unexpected session: 100000 uld: -1 requested by: 50
AppleKeyStore: operation failed (pid: 50 sel: 7 ret: e00002c2 '-536878206'
, -1, 100000)

Any help would be greatly appreciated. It's an old computer but I'm rather fond of it and would love to get it working.